Measuring system for measuring the amount of dielectric in a web

ABSTRACT

An instrument determines one or more physical properties, including dielectric, in a web or other material. A resonant cavity in the instrument resonates at a known band of frequencies. The instrument generates a constant frequency signal within the known band, divides the signal into a measuring signal and a reference signal. With the instrument proximate the web, the measuring signal is passed into the resonant cavity. A first fraction passes through the resonant cavity. incurring a phase shift. A second fraction is reflected from the cavity. The phase shift in the measuring signal is compared to the reference signal, and a first output signal is sent to a controller. The magnitude of the reflected signal is determined, and a second output signal is sent to the controller. Using the first and second output signals, the controller calculates a resultant property value (e.g. moisture content), using the combined values of phase shift and reflected power to cancel out the affect of distance of the e.g. moisture from the resonant cavity. The instrument can also determine length, speed of travel, and temperature of the web, and the controller can combine such measurements mathematically, determining the location in the web of, for example, given readings of moisture and temperature, as well as the general condition of the web.

FIELD OF THE INVENTION

This invention relates to instruments and methods for measuring moistureand other properties extant in a material or web, e.g. a travelling web.

BACKGROUND OF THE INVENTION

This invention pertains to the measurement of moisture and otherrelevant properties extant in a material or web, including, but notlimited to, properties of speed, length, temperature, and vibration.

Hereinafter, the invention is described with respect to its applicationto the detection of moisture and other properties extant in apapermaking felt. It is contemplated that both the instruments of theinvention and the methods of the invention have application to a varietyof situations and materials requiring a non-destructive method ofdetermining moisture content and/or other properties in respectivematerials. While the description concentrates on a travellingclosed-loop web, e.g. a papermaking felt, it is appreciated that similarapplications can be made for other uses, and in other industries, inlight of the description of the invention herein.

In the papermaking industry, it is desirable to periodically determinethe condition of a papermaking felt used in the papermaking process, soas to adjust the operation of the felt or to anticipate, and plan for,replacing the felt. Determining the moisture content of the felt isuseful for determining the effectiveness of operation of the papermakingmachine, and also the condition of the papermaking felt. It is alsodesirable to measure other properties pertaining to the felt, includingspeed and length. As a felt wears it changes size. Hence, periodicallymeasuring the length of a felt provides information useful fordetermining the need to replace, or more closely monitor, a particularfelt.

It is also desirable to measure the temperature of the felt at variouspositions across its width and along its length. In addition to moisturecontent, temperature variations may also indicate equipment problems orthe condition of the felt.

The collection of vibration data is useful for determining if vibrationswithin the papermaking machine can be correlated to moisture or otherproperties in the felt.

Yet another desirable capability for test instruments used inconjunction with papermaking lies in correlating moisture, temperature,and vibration data to specific locations on a particular papermakingfelt. Collecting and storing such data concurrently with speed andlength measurements can provide resultant data useful for making suchcorrelations.

It is also desirable to compare moisture, temperature, and/or vibrationdata for a given location on the felt to manufacturing data for thespecific felt to identify possible anomalies in materials used, ormanufacturing practices.

It is desirable for an instrument used to measure moisture and otherproperties in a material or web to be capable of taking a series ofreadings closely spaced in time, each reading giving a measure of theproperty of interest.

Where a series of readings for a particular property is taken across thewidth of a papermaking felt of other web, the repeat rate of theinstrument as to that property determines the spacing across the widthof the web represented by consecutive readings. The repeat rate for theseveral property measurements differs according to the specifics for therespective sensors and electric circuitry.

It is desirable to standardize the number of data points with respect tothe length of the path along which the data points were collected, forexample along the length of the web, such that each data pointrepresents a fixed, uniformly repeated portion of the length of thepath. The path may, of course, extend across the width of a stationaryor moving e.g. closed loop web. Such standardizing allows historicaldata on a particular felt to be easily compared with a present readingto help identify ongoing changes in the condition of the felt over itsuse life, and changes in the environment in which the felt is operating.

It is an object of this invention to provide methods for determining themoisture in a web or other material.

It is another object to provide methods for determining the condition ofa web through measurement of relevant properties including, but notlimited to, moisture, speed, length, temperature, and vibration.

It is a further object of this invention to provide a method forcorrelating moisture, temperature, and/or vibration data to particularloci on the web.

It is yet another object of this invention to provide methods forobtaining a fixed number of data points independent of the repeat rateor measurement time for a given property measurement.

It is yet a further object of this invention to provide an instrumentfor measuring moisture in a material or web.

It is still another object of this invention to provide a resonantcavity for transmitting a microwave signal into the material in which aproperty is to be measured.

SUMMARY OF THE DISCLOSURE

The invention comprehends novel instruments and methods, for collectingdata and thereby determining the amount of dielectric, includingmoisture, in a material, along with other physical properties, includingstoring dielectric (e.g. moisture) and other properties concurrently,and mathematically manipulating the data in arriving at thedeterminations. The summary and description hereafter refer to atravelling web as the preferred material from which data is collected.The possible uses of the invention are not, however, limited totravelling webs. The invention also applies to static webs, and othernon-web materials. A preferred application of the instrument is todetermine moisture, and indirectly conditions of manufacture and use, ofa papermaking felt.

A first family of embodiments comprises a measuring system for measuringthe amount of dielectric in a web. The measuring system includes ameasuring instrument having an electric circuit, the electric circuitcomprising an electric energy source, for emitting a constant frequencysignal; a power divider for dividing the constant frequency signal intoa reference signal at a reference terminal, for travelling along areference path, and a measuring signal at a measuring terminal, fortravelling along a measurement path; a receptacle comprising a resonantcavity having at least one resonant frequency, the receptacle beingelectrically connected to the electric energy source such that a firsttraversing fraction of the measuring signal, corresponding to the atleast one resonant frequency, traverses along the measurement path,through the resonant cavity, and wherein a second fraction of themeasuring signal is reflected from the resonant cavity, the receptaclebeing positioned in the measuring instrument to accommodate placing theresonant cavity proximate the web, the resonant cavity being adapted tocause a phase shift in the traversing fraction in response to thedielectric in the web, such that the phase of the traversing fraction isshifted relative to the phase of the reference signal, the magnitude ofthe phase shift in the traversing fraction being a function of theamount of dielectric in the web; a phase difference detector forreceiving the reference signal and the first portion of the measuringsignal after the traversing fraction traverses the resonant cavity, thephase difference detector being adapted to detect the difference betweenthe phase of the reference signal and the phase of the traversingfraction and to provide a first output signal, the magnitude of thefirst output signal depending on the magnitude of the difference inphase so detected, the first output signal providing a firstrepresentation of the amount of dielectric in the web; and a reflectedpower detector electrically connected between the receptacle and themeasuring terminal of the power divider, for providing a second outputsignal, the magnitude of the second output signal depending on themagnitude of the reflected second fraction of the measuring signal, thesecond output signal thus comprising a second representation of theamount of dielectric in the web.

In preferred embodiments, the invention comprehends including acontroller adapted to compare the first and second output signals todata stored in the controller, thereby to cancel out the affect of thedistance between the resonant cavity and the dielectric (e.g. moisture)being detected, and to generate a third output signal, the third outputsignal being a more nearly accurate representation of the dielectric inthe web than either of the first and second output signals.

In general, the difference in phase, as detected in the phase differencedetector, is a function of dielectric properties in the web.

Preferably, the electric energy source comprises, in combination, avaractor-tuned oscillator having a third output signal, asingle-frequency crystal oscillator having a fourth output signal, and aphase-locking circuit comprising the varactor-tuned oscillator and thesingle-frequency crystal oscillator, a portion of the third outputsignal being routed through the phase locking circuit, the phase lockingcircuit being configured to synchronize the varactor tuned oscillatorwith the single-frequency crystal oscillator to thereby stabilize thefrequency of the third output signal.

In preferred embodiments, the receptacle comprises a tuned transmissionline in the resonant cavity, preferably first and second transmissionrods, and a variable matching device for altering the reactive impedanceof the resonant cavity. The transmission line typically has input andoutput terminals, the variable matching device comprising a varactordiode electrically connected to at least one of the first and secondtransmission rods at the input terminal.

The receptacle preferably has a plurality of walls, and an open top,including a top surface, the measuring instrument comprising a top wall,e.g. of acrylonitrile butadiene styrene copolymer, propinquant the topsurface, the top wall being adapted to transmit microwave energy fromthe resonant cavity into e.g. a papermaking felt with negligibleattenuation, a known fixed amount of change in phase, and negligiblechange in frequency.

The transmission line is preferably constructed of a material having acoefficient of thermal expansion no greater than 4×10⁻⁶ inch per inchlength degree Celsius at room temperature. A typical such materialcomprises about 60 to about 65 percent by weight iron, about 34 to about39 percent by weight nickel, and about 0.5 to about 1.5 percent byweight manganese.

An exemplary phase difference detector comprises a phase locked loop,including a variable phase shifter having a third output signal; a phasedetector having a fourth output signal, and having as inputs, the thirdoutput signal of the phase shifter, and the first traversing fraction ofthe measuring signal as modified by passage through the resonant cavity;and an integrator having, as an input, the fourth output signal of thephase detector, the integrator providing a fifth output signal,including a control signal to the variable phase shifter for forcing thereference signal and the first traversing fraction to arrive at thephase detector in quadrature, and thereby forcing the output signal ofthe phase detector to a null, the output signal of the integrator, afterachieving the null, being representative of the phase difference betweenthe reference signal and the first traversing fraction of the measuringsignal.

The electric circuit may include a bias tee electrically connectedbetween the measuring terminal of the power divider and the resonantcavity, for providing a bias on the variable matching device, to therebycontrol the sensitivity, of the tuned transmission line, to the amountof dielectric in the web, and to control the ratio between the amountsof reflected power versus traversing power.

The measuring system may further include, in the measuring instrument,first and second switching devices electrically connected to the inputand output terminals, respectively, of the resonant cavity, a firstposition of the switching devices directing the measuring signal to theresonant cavity, a second position of the switching devices directingthe measuring signal to bypass the resonant cavity and pass along analternate signal path, which can provide a phase shift standard,independent of dielectric adjacent the resonant cavity, whereby thefirst output signal of the phase difference detector correlates withphase shift caused by circuit elements within the measuring system.Preferably, the alternate signal path comprises a signal conductor ofknown phase length and know mismatch.

A variable phase shifter, having a variable control input signal, forvarying the phase length of the measurement path, may be connected inseries with the measuring terminal of the power divider, and when thefirst and second switching devices are positioned to bypass the resonantcavity, the phase shifter control input can be varied to change thephase length of the measurement path, thereby compensating for circuiterrors and restoring a known calibration condition prior to takingmeasurements.

The measuring system may include a temperature measuring device,preferably an infrared detector, for measuring temperature in the web,and means to compensate the first output signal for temperaturevariations.

The electric circuit preferably includes at least one attenuation deviceand at least one signal amplification device in series with each of themeasurement path and the reference path, the at least one attenuationdevice in each path being effective to attenuate power reflected backthrough the respective circuit elements toward the power divider, the atleast one signal amplification device in each path being effective tomaintain amplitudes in the respective signals sufficient for detectingthe phase difference between the reference signal and the measuringsignal in the phase difference detector.

Preferably, the reflected power detector comprises a reflected powerbridge having an output signal, and a radio frequency detectorelectrically connected to the reflected power bridge, to measure themagnitude of the output signal from the reflected power bridge, and toprovide an output signal dependent on the magnitude of the output signalfrom the reflected power bridge.

In a second family of embodiments, the invention comprehends a measuringsystem for measuring the amount of dielectric in a web. The measuringsystem includes a measuring instrument having an electric circuit, theelectric circuit comprising an electric energy source, for emitting aconstant frequency signal; a reflection device electrically connected tothe electric energy source, for reflecting a fraction of the signal backthrough the electric circuit; and a reflected power detectorelectrically connected in the electric circuit between the reflectiondevice and the electric energy source, for providing an output signal,the magnitude of the output signal depending on the magnitude of thereflected fraction of the constant frequency signal, the output signalcomprising a representation of the amount of dielectric in the web.

In a third family of embodiments, the invention comprehends a measuringsystem for measuring the amount of dielectric in a closed loop webhaving a length and a width, and traveling at a speed, the measuringsystem comprising a measuring instrument including (i) a dielectricdetector for collecting dielectric readings comprising a first set ofdata relating to dielectric in the closed loop web and generating adielectric signal, and (ii) at least one sensor positioned in saidmeasuring instrument to sense an intermittently occurring propertyextant in a mark extending across the width of the web, thereby tocollect a second set of data useful for determining the length of theclosed loop web; and a data storage device, for storing the second setof data concurrently with the first set of data, thus to provide a firstcomposite set of data, comprising the first and second sets, useful fordetermining physical locations on the web represented by respective onesof the dielectric readings in the first set.

The measuring system preferably includes a controller adapted tomanipulate the first and second sets of data, thereby to determinephysical locations on the web represented by ones of the dielectricreadings in the first set.

The measuring instrument preferably includes a temperature measuringdevice, preferably an infrared sensor, for collecting a third set oftemperature data, the data storage device being adapted to receive andstore the first and second sets of data concurrently with the third set,thus to provide a second composite set of data, comprising the secondand third data sets, representing the physical location on the webrepresented by respective ones of the temperature readings in the thirdset.

The measuring system may include a vibration sensor, for collecting afourth set of data relating to vibration in equipment conveying and/oroperating on the web, the data storage device being adapted to receiveand store the vibration data concurrently with the dielectric, speed,and length, and optionally temperature, data, thus to provide acomposite set of data, representing the physical location on the webrepresented by ones of the readings of the vibration data.

In a fourth family of embodiments, the invention comprehends areceptacle assembly for use in an electronic measuring instrument, thereceptacle assembly comprising a receptacle having a plurality of wallsand an open top, including a top surface. The plurality of walls and thetop surface, in combination, define an open-top resonant cavity. Thereceptacle further includes a tuned transmission line in the resonantcavity, the tuned transmission line being oriented in a plane parallelto the top surface, the transmission line being constructed of materialhaving a coefficient of thermal expansion no greater than 4×10⁻⁶ inchper inch length degree Celsius at room temperature.

The tuned transmission line preferably comprises first and secondtransmission rods, having input and output terminals, and a variablematching device comprising a varactor diode electrically connected to atleast one of the first and second transmission rods at the inputterminal, for altering the reactive impedance of the resonant cavity.Preferably, the material comprising the transmission line is about 60 toabout 65 percent by weight iron, about 34 to about 39 percent by weightnickel, and about 0.5 to about 1.5 percent by weight manganese.

Preferably, the receptacle assembly includes a bias tee, electricallyconnected to the receptacle, for imposing a bias on the variablematching device, to thereby control the sensitivity of the tunedtransmission line.

The receptacle assembly may include first and second switching deviceselectrically connected to the input and output terminals respectively ofthe resonant cavity, a first position of the switching devices directinga signal to pass into the resonant cavity, a second position of theswitching devices directing a signal to bypass the resonant cavity andpass along an alternate signal path, preferably a coaxial signalconductor of known phase length, the alternate signal path thusproviding a phase shift independent of the resonant cavity.

In a fifth family of embodiments, the invention comprehends a method ofcollecting data including an unspecified number of data values, andproviding a fixed number of data points therefrom. The method comprisesthe steps of collecting data values at a given uniform repeat rate ofpreferably at least about 500 readings per second, along a path, thepath having a length; storing a first set of successive ones of the datavalues so collected in a first memory device, as data points, the firstmemory device having a first capacity to store data points in a firstfixed number of data receiving elements corresponding to the number ofdata points in the first set; after storing the first set of data pointsin the first memory device, collecting and storing successive datavalues as a second set in a second memory device, as data points, thesecond memory device having a second capacity to store data points in asecond fixed number of data receiving elements; and after storing anumber of successive data points of the second set in the second memorydevice, dithering the first and second sets of data points into thefirst memory device while maintaining the sequence in which the datavalues were collected, thereby arriving at a resultant third set ofcalculated data points in the first memory device, and storing the thirdset of data points in the first memory device, the number of data pointsin the third set being equal to the first fixed number of data elements.

In some embodiments in this family, the method comprises, prior tostoring the recited second set of data points in the second memorydevice, storing, in the second memory device, as the second set of datapoints, a number of the data values sufficient to fill the second memorydevice; and dithering the first and second sets of data points into thefirst memory device while maintaining the sequence in which the datavalues were collected, thereby arriving at a resultant dithered set ofcalculated data points in the first memory device, and storing theresulting dithered set of data points in the first memory device, thenumber of data points in the dithered set of data points being equal tothe first fixed number of data elements.

In those embodiments where the number of data points in each of thefirst and second data sets are equal, the method preferably includes thestep, after storing the second set of data points in the second memorydevice, of averaging each successive two data points in the combinationof the first and second memory devices, to thereby obtain a third set ofdata points having resultant average values, and storing the third setof data points in corresponding data elements of the first memorydevice.

The method may include the step of averaging a number of successive datavalues equal to the number of data values previously averaged and storedin ones of the data elements of the first memory device, to obtain adata point having a respective average value, and so averagingsuccessive data values, to thereby obtain a fourth set of data pointshaving respective resultant average values, and storing the fourth setof data points in corresponding data elements of the second memorydevice and, after filling the second memory device, repeating the abovesteps until the step of collecting data values is terminated, and then,after the step of collecting data values is terminated, dithering theremaining data points, as extant in the second memory device, into thefirst memory device, thereby arriving at a composite data set in thefirst memory device, and storing the composite data set in the firstmemory device such that the data in the first memory device maintainsthe sequence in which the data values were collected, the number of datapoints in the composite data set being equal to the first fixed numberof data elements.

In a sixth family of embodiments, the invention comprehends a method ofcollecting data along a path, and identifying discrete fractions of thedata so collected to discrete fractions of the path. The methodcomprises the steps of collecting data values at a given uniform repeatrate along the path, including sensing data values representing aperiodically repeating reference element; storing a first set ofsuccessive ones of the data values so collected in a first memorydevice, as data points, the first memory device having a first capacityto store data points in a first fixed number of data receiving elementscorresponding to the number of data points in the first set; afterstoring the first set of data points in the first memory device,collecting and storing successive data values as a second set in asecond memory device, as data points, the second memory device having asecond capacity to store data points in a second fixed number of datareceiving elements; after storing a number of successive data points ofthe second set in the second memory device, dithering the first andsecond sets of data points into the first memory device whilemaintaining the sequence in which the data values were collected,thereby arriving at a resultant third set of calculated data points inthe first memory device, and storing the third set of data points in thefirst memory device, the number of data points in the third set beingequal to the first fixed number of data elements, the data valuesrepresenting the reference element thus separating the data points inthe third data set into data subsets; and, with the data so separatedinto subsets, correlating at least one of the data points in a givensubset to a specific fraction of the path, the fraction having a lengthcomprising, as a fraction of the length of the path, a numeratorcorresponding to the number of data points in the given subset which arebeing correlated, and a denominator equal to the number of data pointsin the given subset.

In a seventh family of embodiments, the invention comprehends a methodof measuring the amount of moisture in a web. The method comprises thesteps of generating an electric signal having a constant frequency;dividing the electric signal into a reference signal and a measuringsignal; passing the measuring signal into a receptacle comprising aresonant cavity, the resonant cavity being proximate the web, a firsttraversing fraction of the measuring signal traversing the resonantcavity, a second reflected fraction of the measuring signal beingreflected from the resonant cavity, moisture in the web causing a phaseshift in the traversing fraction, the magnitude of the phase shift beinga function of the amount of moisture in the web, the magnitude of thereflected fraction being a function of the amount of moisture in theweb; detecting, in a phase difference detector, the difference in phasebetween the reference signal and the traversing fraction; providing afirst output signal from the phase difference detector, the magnitude ofthe first output signal depending on the magnitude of the difference inphase so detected between the reference signal and the traversingfraction, the first output signal providing a first representation ofthe amount of moisture in the web; measuring, in a reflected powerdetector, the magnitude of the reflected fraction of the measuringsignal; and providing a second output signal from the reflected powerdetector, the magnitude of the second output signal depending on themagnitude of the reflected fraction of the measuring signal, the secondoutput signal comprising a second representation of the amount ofmoisture in the web.

The method preferably includes measuring the temperature of the web, andcompensating the first and second output signals for temperaturevariation from a standard, and comparing the first and second outputsignals to data indicating the affect of distance on the amount of thephase shift and the amplitude of the reflected fraction, andmathematically cancelling out the affect, on the first and second outputsignals, of distance between the resonant cavity and the moisture in theweb.

In an eighth family of embodiments, the invention comprehends a methodof measuring the amount of moisture in a web, using an electricalinstrument. The method comprises the steps of generating an electricsignal having a constant frequency; dividing the electric signal into areference signal and a measuring signal; positioning, propinquant theweb, an electrical reflection device adapted to reflect an electricsignal back through the electric circuit, wherein the magnitude of thereflected signal depends on the amount of moisture in the web, andinputting the measuring signal to the reflection device, a fraction ofthe measuring signal being reflected back from the reflection device;receiving, in a radio frequency detector, the reflected fraction of themeasuring signal, and measuring the magnitude of the reflected fractionso received; and providing an output signal from the radio frequencydetector, the magnitude of the output signal depending on the magnitudeof the reflected fraction, the output signal from the radio frequencydetector being a representation of the amount of moisture in the web.

The method preferably includes measuring the temperature of the web, andcompensating the output signal for temperature variation from astandard.

In a ninth family of embodiments, the invention comprehends a method fordetermining the condition of a closed loop web, the web having a lengthand a width, and travelling at a speed. The method comprises the stepsof collecting a first set of data values relating to moisture content inthe closed loop web; sequentially sensing an intermittently occurringproperty extant in a mark extending across the width of the web, therebycollecting second and third sets of data useful for determining thespeed and length of the closed loop web; and storing the second andthird sets of data concurrently with the first set, thus providing acomposite set of data, comprising the first, second, and third sets,useful for determining the physical location on the web represented byones of the moisture readings in the first set.

The method preferably includes repeatedly sensing the temperature of theclosed loop web and thereby collecting a fourth set of temperature data,and storing the second and third sets of data concurrently with thefourth set, providing a second composite set of data, comprising thesecond, third and fourth sets, for representing the physical location onthe web represented by ones of the points of data in the fourth set.

The invention may include collecting a set of vibration data useful fordetermining the relationship between the closed loop web and equipmentconveying and/or operating on the web, and storing the first and secondsets of data concurrently with the vibration data, and preferablyincludes computing a moisture frequency spectrum from the moisture data,computing a vibration frequency spectrum from the vibration data,comparing the moisture and vibration frequency spectra to detectsimilarities indicating that vibration could be related to moisture inthe web, and using the comparison of the moisture and vibrationfrequency spectra, in combination with the speed and length data, torelate the moisture data to a physical location in the web, henceidentifying a locus, in the closed loop web, representing a potentialsource of vibration, and comparing the locus of potential vibration tomanufacturing data for the specific web, to assist in identifyinganomalies in materials, or manufacturing practices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representative schematic circuit diagram of circuitryused in a measuring instrument of the invention.

FIG. 2 shows a pictorial view of a receptacle used in an instrument ofthe invention.

FIG. 3 shows a side elevation, with parts cut away, of a portion of aninstrument of the invention.

It is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is capable of other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the terminology and phraseology employed herein is for purpose ofdescription and illustration and should not be regarded as limiting.Like reference numerals are used to indicate like components.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now by characters of reference to the drawings, FIG. 1 showsan electric circuit 1, for use in an instrument 10 of the invention, todetermine moisture and other properties in a web 12, shown in FIG. 3.Referring again to FIG. 1, a high frequency electric energy source 14provides a constant frequency (e.g. microwave frequency) signal to apower divider 16. The power divider 16 divides the signal from theenergy source 14 into a measuring signal and a reference signal, bothoutputted from power divider 16 at respective measuring and referenceterminals (not shown). The measuring signal is passed, through bufferamplifier 18, to variable phase shifter 22. The reference signal ispassed, through buffer amplifier 20, to variable phase shifter 21.Buffer amplifiers 18, 20 provide RF isolation within the circuit 1, andamplify the respective reference and measuring signals. The arrowheadsin the line circuit diagram of FIG. 1 indicate the general direction offlow of power through the circuit.

Variable phase shifter 22 is electrically connected, through bufferamplifier 24, to reflected power detector 26. The function of bufferamplifier 24 is similar to that of buffer amplifiers 18, 20, previouslydescribed. Reflected power detector 26 is electrically connected to biastee 28. The bias tee is electrically connected to a receptacle 32 (SeeFIGS. 2 and 3) through switch 30A. Receptacle 32 is electricallyconnected through switch 30B to RF pad 34, and from RF pad 34 to phasedifference detector 36. Switches 30A and 30B are shown in the defaultswitch position in FIG. 1, wherein a signal is passed through thereceptacle 32 to sense e.g. moisture. In the alternate positions ofswitches 30A, 30B not shown, the measuring signal passes through acalibration line 51 of stable, and known, phase length. Calibration line51 may be e.g. a coaxial cable of known phase length, relative to thefrequency of the signal outputted from energy source 14.

Referring now to FIG. 2, receptacle 32 includes two end walls 38, 40,two side walls 42, 44, a bottom wall 46, a top surface 48, an open top,and a resonant cavity 50 defined between the end walls, side walls,bottom wall, and the open top. Parallel tuned transmission rods 52traverse the length of the receptacle 32, in the resonant cavity 50,between end walls 38 and 40. A varactor diode 54 is mounted toreceptacle 32, in cavity 50, adjacent end wall 40, and is electricallyconnected in series to one of the tuned transmission rods 52 adjacentend wall 38.

With switches 30A, 30B aligned in the default position as shown, themeasuring signal passes from bias tee 28, through switch 30A, into theresonant cavity. A first traversing fraction of the measuring signaltraverses through the resonant cavity by way of transmission rods 52,through switch 30B, to RF pad 34. RF pad 34 functions to attenuate themeasuring signal and thereby to reduce the amount of reflected powerreaching the surrounding circuit elements.

A second reflected fraction of the measuring signal is reflected fromthe resonant cavity back through bias tee 28 to the reflected powerdetector 26.

Moisture present in the web 12 causes a phase shift in the traversingfraction of the measuring signal, the amount of the phase shift being afunction of the amount of moisture in the web. The amount of moisture inweb 12 also affects the magnitude of the reflected fraction of themeasuring signal.

The varactor diode 54 receives its input signal from bias tee 28,through switch 30A, and supplies its output signal to the tunedtransmission rods 52, thereby operating as a variable impedance matchingdevice. Varying the bias on the variable matching device 54 through biastee 28 affects the impedance mismatch in the cavity. The impedancemismatch controls the ratio of the amount of power transmitted throughthe resonant cavity 50 to the amount of power reflected from the cavity,and in addition, controls the amount of phase shift resulting frommoisture in the web.

The output signal of the RF pad 34 passes into phase difference detector36 at phase detector 56. Phase difference detector 36 has, as inputs,the traversing fraction of the measuring signal as outputted from RF pad34, and the reference signal as outputted from buffer amplifier 20.Phase difference detector 36 measures the difference in phase betweenthe reference signal, as outputted from buffer amplifier 20, and thetraversing fraction of the measuring signal as outputted from RF pad 34,and provides, as an output signal, a first property signal giving afirst representation of the amount of moisture in the web.

The reflected power detector 26 measures the magnitude of the reflectedsecond fraction of the measuring signal and provides, as an outputsignal, a second property signal, independent of the first propertysignal outputted from phase difference detector 36, giving a secondrepresentation of the amount of moisture in the web. Thus, the phasedifference detector 36 and the reflected power detector 26 give firstand second different, and independent representations of the amount ofmoisture in web 12.

The outputs of the phase difference detector 36 and the reflected powerdetector are inputted to the computer controller 58. The computercontroller has stored, in its memory, a first equation defining therelationship between the output of the phase difference detector and themoisture in the web, and a second equation defining the relationshipbetween the output of the reflected power detector and the moisture inthe web. However, neither equation, used alone, accounts for the affectof distance between the resonant cavity and the moisture being detected.Using the inputs from the phase difference detector and the reflectedpower detector, the computer controller simultaneously solves the twoequations, which have two unknowns, to arrive at a more precisecalculated representation of the amount of moisture in the web. Thiseffectively cancels out the affect of distance between the cavity andthe moisture in the web, thus giving a more precise indication of theactual amount of moisture than either of the signals, outputted from thephase difference detector and the reflected power detector, alone.

The phase difference detector 36 comprises a phase-locked loop includingthe variable phase shifter 21, buffer amplifier 60, phase detector 56,and integrator 62. The phase detector 56 receives, as inputs, the outputof buffer amplifier 60, representing the reference signal, and theoutput from RF pad 34, representing the traversing fraction of themeasuring signal. The output of phase detector 56, representing thephase difference between the reference signal, and the traversingfraction of the measuring signal, is inputted to the integrator 62. Themagnitude of the output of phase detector 56 depends on the magnitude ofthe phase difference between the reference signal and the traversingfraction of the measuring signal, as inputted from buffer amplifier 60and RF pad 34, respectively. Integrator 62 provides, as an output, acontrol signal, the magnitude of which is dependent on the magnitude ofthe signal outputted from phase detector 56, to variable phase shifter21, and thereby changes the phase angle of the signal outputted from thevariable phase shifter 21. With the phase angle of the reference signalthus modified, the combination of the reference signal and thetraversing fraction of the measuring signal force the output of thephase detector 56 to a null. The output of the integrator 62, afterachieving the null at phase detector 56, is representative of theoriginal phase difference between the output of phase shifter 21,representing the reference signal, and the output of the RF pad 34,representing the traversing fraction of the measuring signal. As shownin FIG. 1, a portion of the output signal from integrator 62 is fed tocomputer controller 58, as the first representation of the amount ofmoisture in web 12.

High frequency electric energy source 14 includes a varactor-tunedoscillator 64 and a crystal phase lock 66. A portion of the output ofthe varactor-tuned oscillator 64 is routed through the crystal phaselock 66, thereby synchronizing the varactor-tuned oscillator 64 with asingle-frequency quartz crystal, having a frequency which is a fixedfraction of the frequency of oscillator 64, in the crystal phase lock66, thereby stabilizing the output of the varactor-tuned oscillator 64.

Reflected power detector 26 comprises a reflected power bridge 68, whichreceives the reflected fraction of the measuring signal from resonantcavity 50, through switch 30A and bias tee 28, and provides an output toradio frequency detector 70. Radio frequency detector 70 converts theoutput of the reflected power bridge 68 from a radio frequency (e.g.microwave) signal to a direct current signal, the magnitude of thesignal outputted from the radio frequency detector 70 being dependent onthe magnitude of the power reflected from the resonant cavity 50.

FIG. 3 shows, in side elevation view, a cross section of a portion ofthe measuring instrument 10, illustrating the receptacle 32 andappurtenances, in position closely adjacent a web 12 in which moistureand other properties are to be measured. FIG. 3 views web 12 fromgenerally the side of the web, such that the web traverses theinstrument 10 from left to right, as shown by arrow 71. In use, the topwall 72 is generally placed in contact with the web 12.

In a preferred instrument 10, both the receptacle 32 and the circuit 1are designed such that the resonant frequency of the resonant cavity 50is rather stable. Thus, when the instrument is manufactured, specificmaterials and structures are used which contribute to consistency of theresonant frequency. Once the manufacture of a given instrument iscomplete, the instrument is initially calibrated for the resonantfrequency of the specific resonant cavity in that specific instrument.With respect to the resonant frequency of the cavity 50, the frequencyis specifically related to dimensions of the end walls, side walls, andbottom wall, as well as to the dimensions, placement, and the like oftuned transmission rods 52.

In preferred receptacles 32, the side walls 42, 44, end walls 38, 40,and bottom wall 46, are all constructed of nickel-plated steel. Thesteel has limited coefficient of thermal expansion. Transmission rods 52are constructed of a specially selected material which has a very lowcoefficient of thermal expansion, whereby the contribution of the rodsto resonance is generally unaffected by temperature.

For rods 52, the coefficient of thermal expansion is preferably no morethan about 4×10⁻⁶ inch per inch length degree Celsius at roomtemperature. An example of such a material comprises about 60 to about65 percent by weight iron, about 34 to about 39 percent by weightnickel, and about 0.5 to about 1.5 percent by weight manganese. Suchmaterial is available under the Tradename INVAR® as e.g. INVAR 36 fromFry Steel Company, Santa Fe Springs, Calif. INVAR 36 has a chemicalanalysis of about 62 percent iron, about 36 percent nickel, and about 1percent manganese, about 0.25 percent selenium, about 0.28 percentsilicon, and about 0.08 percent carbon.

Top wall 72 of the instrument serves as an interface between the topsurface 48 of the receptacle and the web 12, and thus covers the opentop of the receptacle. Top wall 72 is preferably made with materialwhich readily transmits microwave energy, with negligible attenuation,with known fixed amount of change in phase, and with negligible changein frequency. In addition, the top wall should have a low dielectricconstant. A dielectric constant of no greater than about 5 is preferred,with a dielectric constant of no greater than about 3 being morepreferred. While a variety of polymeric and other such materials cansatisfy the above parameters, and thus can be used, preferred materialsare acrylonitrile butadiene styrene copolymer, epoxy resin, andpolyester fiberglass.

Referring again to FIG. 3, two pairs of optical sensors 74, 76 aredisposed on opposing sides of the receptacle 32, adjacent but spacedfrom the top surface 48, such that the optical sensors 74, 76 areadjacent but spaced from the web 12 when the instrument is being used asshown in FIG. 3. Only one sensor of each pair is shown. As disposed inthe instrument 10, and as suggested by FIG. 3, each pair of opticalsensors is preferably aligned transverse to the transmission rods 52,and thus is aligned perpendicular to the direction of travel of web 12.

The purpose of the optical sensors 74, 76 is to sense a line 78 or othermark, or marks, e.g. generally extending across the width of the web asthe line intermittently passes the optical sensors during normaltraverse of the web from left to right as the web is being used on apapermaking machine, and as illustrated in FIG. 3. Line 78 can be adashed line, or other intermittently structured line. The sensors 74, 76feed the sensed information to the computer controller 58. Preferably,the instrument 10 is held against the web long enough for at least thesensors 74 to read a such line 78 at least twice as the web istravelling in its closed loop path.

Computer controller 58 uses the amount of time for the line to travelthe known distance from the first pair of sensors 74 to the second pairof sensors 76, to compute the speed at which the web is travelling. Thecomputer controller uses the amount of time for a given line 78 to besensed twice by the same optical sensors (e.g. 74), in combination withthe computed web speed, to determine the length of the web.

A temperature sensor 80 is also disposed in adjacent but spaced from thetop surface 48 of the receptacle 32, such that the temperature sensor 80is also adjacent but spaced from the web 12 when the instrument 10 isbeing used to collect data about the web, as shown in FIG. 3. Apreferred temperature sensor senses the temperature of the web withoutcontacting the web. A suitable such temperature sensor is an infraredsensor. An infrared sensors is preferred because infrared sensorsmeasure temperature without contacting the web, and thus the temperatureso read is not affected by frictional contact with the (e.g. moving)web.

The temperature so sensed is inputted to computer controller 58. In theembodiments contemplated, the temperature is repeatedly sensed, so as toprovide a profile of temperature across the width of the web 12, oralong the length of the web, in accord with the relative path traversedby the instrument 10 with respect to the web 12.

The response time of the circuit, namely the time interval betweensuccessive output readings of the computer controller 58, as to moisturecalculated from output signals from the phase difference detector andthe reflected power detector, is limited only by the response time ofthe phase locked loop in the phase difference detector 36. In preferredembodiments, the repeat rate of the circuit is at least 300 readings persecond, preferably at least 500 readings per second. Repeat rates of1000, 2000, 3000, 4000, and in excess of 5000 readings per second arecontemplated as being possible.

In order for the instrument 10 to provide reliable readings as tomoisture content of the web 12, the instrument must be calibrated, inorder to provide standard references against which readings are takenand results are calculated. The calibration has two phases.

The first phase of the calibration function is performed with thereceptacle 32 switched into the circuit. With switches 30A, 30B set inthe default settings, the control input to bias tee 28 is first adjustedto give the desired amount of mismatch to varactor diode 54, therebyadjusting the sensitivity of the resonant cavity 50, to moisture, to aconvenient scale, as well as affecting the relative amounts of thetraversing fraction and the reflected fraction of the signal. Then thecontrol signal to phase shifter 22 is adjusted to bring the output ofintegrator 62 to a preferred level, e.g. 4.1 volts. Thus is the variablephase shifter 22 employed to correct for circuit deviations or drift,using phase shifter 22 to vary the phase length of the measuring path,and thus to bring the output of the integrator 62 to the preferredlevel.

Switches 30A, 30B are then set to the alternate settings, whereby themeasuring signal passes, from switch 30A to switch 30B, through thecalibration line 51 to measure and thereby establish a referencestandard e.g. at about 2 volts. The reflected power caused by theimpedance mismatch in the calibration line circuit is also read andrecorded by computer controller 58. This concludes the initial fieldcalibration of the instrument. The instrument is further calibrated onthe fly during routine use, as discussed later herein.

With respect to the phase shifting function of the circuit, calibrationline 51 provides a route of known phase delay independent of moisture,whereby the output signal of phase difference detector 36 depends onlyon phase shifting caused by circuit elements outside resonant cavity 50.Thus is the net phase shift affect of the circuit elements outside theresonant cavity isolated from the phase shift caused by the resonantcavity.

When the circuit is then returned to the use mode by switching theresonant cavity back into the circuit, any deviation of the output ofthe integrator 62, from the reference (e.g. 4.1) voltage is caused bythe cavity 50, and specifically by the moisture in the web 12 as the webpasses by the cavity 50.

Still referring to the calibration mode, phase two, of the instrument,the calibration line circuit, from and including switches 30A, 30B,through the calibration line 51, includes a known amount of impedancemismatch. With the signal routed through the coaxial calibration line51, the known amount of impedance mismatch causes reflection of aportion of the measuring signal back through bias tee 28, throughreflected power bridge 68, to the radio frequency detector 70. Theamount of reflection received from the known standard amount ofimpedance mismatch provides a standard against which the amount ofreflection from resonant cavity 50 may be measured. The calibrationreading is inputted to computer controller 58.

In phase one of calibration, the switches 30A, 30B are aligned as shownin FIG. 1 to pass the measuring signal through the resonant cavity 50. Avarying control signal is supplied through bias tee 28 to change thereactive impedance of the variable matching device 54, thereby to setthe ratio of the traversing fraction of the measuring signal to thereflected fraction of the measuring signal. The control signal suppliedto bias tee 28 is varied until the reflected power measured by thereflected power detector 26 reaches its lowest point, resulting in areflected power measurement representing a desired value for thecircuit 1. The desired value is then inputted to controlling computer 58and used as a reference for later measurements of reflected power andphase difference.

The calibration function, both phases one and two, is performed inambient conditions, away from concentrations of moisture, for example,pointed away from a moist web such as a moist felt on a papermakingmachine. The calibration mode is preferably entered manually by theoperator of the instrument before, and optionally after, using theinstrument to collect a moisture reading, in order to assure that thecircuit has not drifted away from the calibration point while thereadings were being taken.

The control signal input to phase shifter 22 is maintained while theinstrument 10 is in use taking moisture readings at the web 12. Thecontrol signal to phase shifter 22 thus provides a standard for use inanalyzing the phase shift in the traversing fraction as the traversingfraction advances along the measuring path through the resonant cavity,to the phase difference detector. By varying the control input to thephase shifter 22 in calibrating the instrument 10, phase shift due tocircuit elements can be set and/or restored to a known calibrationcondition prior to taking measurements with the instrument 10.

To this point, the teaching has, in general, focused on the process forgenerating a first reading from the phase difference detector,simultaneously generating a second reading from the reflected powerdetector, and simultaneously feeding the first and second readings tothe computer controller, with the computer controller calculating aresultant moisture data value based on the combination of the first andsecond readings.

In practice, the instrument 10, including the computer controller,repeatedly computes such resultant moisture data values at a high repeatrate. While a wide range of repeat rates is possible, in a preferredinstrument 10, the repeat rate is 512 readings per second.

Still referring to a preferred embodiment, computer controller 58includes first and second memory devices, not shown, to record datavalues for each reading, each memory storage device having 512data-receiving elements. As the instrument reads moisture data values,and the computer controller calculates moisture data points fromrespective such data values, the first 512 such data points are stored,in the sequence received, and as calculated, as a first set of datapoints in the first memory device. The second 512 data values aresimilarly arrived at and stored, as a second set of data points, in thesequence received, and as calculated, in the second memory device. Oncethe second memory device is full, the 512 sequential pairs of datapoints in the first and second memory devices are averaged, and arestored in the first memory device, each of the data points then in thefirst memory device representing two phase shift data values and tworeflected power data values, received from the circuit 1, andcorresponding two calculated data points, as calculated by computercontroller 58.

As additional readings are taken, and passed to computer controller 58,the computer controller averages each successive two such data values toderive data points therefrom, before storing the resulting data pointsin respective data receiving elements in the second memory device. Whenthe second memory device is again full, each data point in each of thefirst and second memory devices represents two data values, each datavalue being computed from the combination of one phase shift input andone reflected power input, from the circuit 1. The 512 sequential pairsof data points in the first and second memory devices are againaveraged, and are again stored in the first memory device, each of thedata points in the first memory device then representing four phaseshift data values and four reflected power values, received from thecircuit 1, and corresponding four calculated data points, as calculatedby computer controller 58.

As additional readings are taken, and passed to computer controller 58,the computer controller averages successive data values, the number ofdata values averaged being equal to the number data values representedby the data points then in storage in the first memory storage device,before storing the data values as data points in respective datareceiving elements in the second memory device. Each time the secondmemory device is filled up, the data points in the second memory deviceare averaged into the first memory device.

When collection of readings stops, the second memory device typicallycontains less than 512 data points. The data points in the second memorydevice are then dithered into the first memory device. The resulting 512data points each represent 1/512th of the length of the path over whichreadings were taken.

The above method of receiving and storing data points provides a methodof receiving an unspecified number of data values, and converting theunspecified number of data values into a pre-determined fixed number ofdata points, each representing the same number of data values. Byrecording the starting and ending point on the web for which readingswere taken, the path along the web can be divided into 512 fractions ofequal length, and each data point in the first memory device can becorrelated to a respective one of such fractions. The path may, ofcourse traverse along the length of the web, along the width of the web,or at an angle traversing both length and width.

Papermaking felts typically include a visual reference line 78, e.g. acolored line, extending across the web, which can be sensed by opticalsensors 74, 76. In preferred embodiments, computer controller alsoreceives, in addition to moisture signals from phase difference detector36 and reflected power detector 26, sensory signals, indicating thepassage of line 78, from the optical sensors. When the computercontroller 58 receives and stores the data points as indicated above, itfirst creates separate subsets of data points, each subset representingthe data values received between successive passes of the line 78 pastthe optical sensors. Thus, each subset of data points represents e.g. acomplete length of the web 12.

Line 78 may take on a range of characters. Thus, it may be intermittent.It may have readability other than optical/visual. The importantproperty is that the line 78 be readable by sensors 74, 76, therespective sensors being sensitive to the readable property of the line78.

Wherever in this teaching, and in the claims following, reference ismade to storing first and second sets of data points in respective firstand second memory devices, the inventors contemplate that a selectednumber of data values may be mathematically altered/modified (e.g.averaged) to arrive at the data points to be stored in the first and/orsecond memory devices. Combining data points from the first and secondmemory devices into the first memory device and subsequent gathering andstoring of data, is then done with consideration for suchalterations/modifications.

Periodically, and especially between calculations which alter or modifydata points and correspondingly move data points from the first andsecond memory devices into the first memory device, the instrument 10automatically makes on-the-fly calibrations, switching in thecalibration line 51 for a brief period, to check and correct for anydrift that may have occurred in circuit 1 since the previouscalibration. Such on-the-fly correction is facilitated by using highspeed switching diodes in high speed electronic switches 30A, 30B. Highspeed switching diodes effectively isolate the moisture affect on thecavity from the calibration line signal during the on-the-flycalibrations.

Simultaneously with the taking of moisture readings as discussed above,the temperature of the web is sensed using infrared detector 80, and thetemperature readings are inputted to computer controller 58. Thecomputer controller then adjusts the data values for temperature, usingknown relationships, before storing the data values in the memorydevices as data points.

Vibration sensors, not shown, can be installed at strategic locations onweb handling equipment used to convey or operate on the web 12, thus tosense vibration of the web handling equipment. The vibration readingscan then be fed into the computer controller 58 simultaneously with therest of the data discussed above, thus enabling the computer controllerto correlate vibration data to specific locations on the web in the samemanner as moisture and temperature data are correlated to specificlocations on the web.

Given the combined readings regarding moisture content, temperature, andvibration, correlated to specific loci on the web, one can then identifyanomalous readings on the web, such as locations where the web is weak,or is wearing more rapidly than anticipated. Given the identity of suchanomalous loci, the manufacturing and supply records related tomanufacture of that specific web can then be reviewed to correlate,where appropriate, the anomalous data to specific raw material suppliesor to manufacturing practices.

It is contemplated that the operation and functions of the inventionhave become fully apparent from the foregoing description of elements,but for completeness of disclosure the usage of the invention will bebriefly described.

With the instrument 10 turned on and warmed up, and away from the web,the input to the bias tee 28 is first adjusted to give the desiredamount of mismatch to varactor diode 54, thereby adjusting thesensitivity of the resonant cavity 50, to moisture, to a convenientscale, as well as affecting the relative amounts of the traversingfraction and the reflected fraction of the signal. Then the input tophase shifter 22 is adjusted until the output of the integrator is 4.1volts.

The switches 30A, 30B are then switched to the alternate position, andthe constant frequency signal from power divider 16 is passed throughthe calibration line to establish a calibration standard at about 2volts. With switches 30A, 30B in the alternate position, the reflectedpower caused by the impedance mismatch in the calibration line circuitis also read and recorded by computer controller 58. This concludes theinitial field calibration of the instrument. The instrument is thenready to read the moisture in the web 12.

Next, the instrument 10 is placed against a surface of the web 12,bringing the resonant cavity 50 propinquant the web, and respectivelythe moisture in the web. At that point, the cavity 50 is separated fromthe web and its moisture only by the top wall 72. With the instrument sopositioned against the web, readings are taken and stored as discussedabove. The readings include moisture readings, optical readings withrespect to reference line 78, vibration in the web handling equipment,and temperature readings. The moisture readings and the temperaturereadings are stored separately, and are both correlated to passings ofthe reference line 78 past optical sensors 74, 76. Accordingly, computercontroller 58 compensates each moisture reading for the temperaturesensed at the infrared detector 80. Also, the computer controller cancorrelate each moisture reading to the temperature of the web at thelocus where the respective reading was taken.

Thus can a series of readings be used to simultaneously determinemoisture content of the web, temperature of the web, vibration relatedto the web, length of the web, and web speed. Given length of the web,the computer controller 58 can correlate specific moisture and the likedata values to specific respective segments of the web along the pathwhere readings were taken, as a given fraction of the length of the web,whereby each such data point correlates with a specific segment of theweb.

The phase shift occurring in cavity 50 is caused by the dielectric ofthe water, which is significantly greater than the phase shift caused byionics or other impurities typically encountered in the water used on apapermaking felt in a papermaking machine, as well as beingsignificantly greater than phase shift caused by materials typicallycarried in or on the web, such as a plastic substrate, wool, or otherfiber batting, and e.g. cellulose in the paper being formed on the web.

The frequency of the signal generated at oscillator 64 is preferably inthe range known as microwave frequency, in order to take advantage ofthe sensitivity of microwave frequency signals to dielectric of anymaterial into which the signal passes. Since the response of the circuitdepends on dielectric, instruments of the invention can be used tosense/measure any property which varies in intensity with the dielectricof the material of interest.

The instrument, as illustrated, records 512 moisture readings persecond. While temperature is preferably simultaneously recorded, themaximum repeat rate on the temperature reading is controlled by themaximum repeat rate of the temperature sensor, which may be less thanthe repeat rate for circuit 1. Thus, for a given data point, therespective temperature reading may lag the repeat rate for the moisturereading.

As referred to herein, "dithering" and the like generally comprehendsconverting a higher number of data points to a lower number of datapoints, providing resultant data points at a lower resolution, amountingto a form of data compression. Thus, where the number of data points inthe second memory device is the same as the number of data points in thefirst memory device, dithering comprehends treating the combination ofthe data points in the first and second memory devices as a unit,averaging pairs of successive data points in both the first and secondmemory devices, and combining the resultant averaged data points socalculated, part from the first memory device, part from the secondmemory device, into the first memory device, all while maintaining thesequence in which the data values were collected.

Where the number of data points in the second memory device is less thanthe number of data points in the first memory device, the data points inboth of the first and second memory devices are treated as a unit,compressed to 512 data points, reflecting the number of data storageelements in the first memory device, and stored in the first memorydevice. The actual mechanism for compressing the data points can vary.In one compression embodiment, each of the resultant e.g. 512 datapoints represents an average of a fractional number of successive datapoints, or fractions of data points, corresponding to the compressionratio. In this embodiment, each one of the resultant 512 data pointsrepresents a common fraction of the length of the path over which thedata values were collected.

In a second compression embodiment, the number of data points, in thesecond memory device, which must be averaged into the first memorydevice, is first determined. Then that number of averages of successivedata points are calculated, evenly spread over the combined set of datapoints of the first and second memory devices, to arrive at thecompressed resultant set of 512 data points, and the resultant 512 datapoints are stored in the first memory device. In this embodiment, someof the resultant data points in the first memory device represent moredata values than other resultant data points. Thus, each data pointrepresents one of first and second different fractions of the length ofthe path over which the data values were collected. Where there are 512resultant data points, the first fraction is greater than 1/512, and thesecond fraction is less than 1/512.

The fixed number of data elements in the respective memory devices canbe based on hardware limitations, software-imposed limitations, or acombination of hardware and software limitations.

As contemplated herein, computer controller 58 is a digital controlmodule integral in instrument 10, which is a portable, hand-held deviceweighing less than e.g. 10 pounds, preferably less than 5 pounds.

As referred to herein, "data values" generally relate to values receivedfrom circuit 1 prior to mathematical manipulation by computer controller58, whereas "data Points" generally relate to such values aftermathematical manipulation by the computer controller, e.g. to compensatefor temperature or other non-moisture variable, or to dither informationfrom the first and second memory devices into the first memory device.

The first and second memory devices are discussed above with respect tostoring moisture data. Corresponding additional first and second memorydevices can, and preferably are, used to store temperature, vibration,speed, length, and like data, in like manner, for use in the severalcalculations.

Those skilled in the art will now see that certain modifications can bemade to the apparatus and methods herein disclosed with respect to theillustrated embodiments, without departing from the spirit of theinstant invention. And while the invention has been described above withrespect to the preferred embodiments, it will be understood that theinvention is adapted to numerous rearrangements, modifications, andalterations, and all such arrangements, modifications, and alterationsare intended to be within the scope of the appended claims.

Having thus described the invention, what is claimed is:
 1. A measuringsystem for measuring the amount of dielectric in a web, said measuringsystem including a measuring instrument having an electric circuit,including a plurality of circuit elements, said electric circuitcomprising:(a) an electric energy source, for emitting a constantfrequency signal; (b) a power divider for dividing the constantfrequency signal into a reference signal at a reference terminal, fortravelling along a reference path, and a measuring signal at a measuringterminal, for travelling along a measurement path; (c) a receptaclecomprising a resonant cavity having at least one resonant frequency,said receptacle being electrically connected to said electric energysource such that a first traversing fraction of the measuring signal,corresponding to the at least one resonant frequency, traverses alongthe measurement path, through said resonant cavity, and wherein a secondfraction of the measuring signal is reflected from said resonant cavity,said receptacle being positioned in said measuring instrument toaccommodate placing said resonant cavity proximate the web, saidresonant cavity being adapted to cause a phase shift in the traversingfraction in response to the dielectric in the web, such that the phaseof the traversing fraction of the measuring signal is shifted relativeto the phase of the reference signal, the magnitude of the phase shiftin the traversing fraction of the measuring signal being a function ofthe amount of dielectric in the web; (d) a phase difference detector forreceiving the reference signal and the traversing fraction of themeasuring signal after the traversing fraction traverses said resonantcavity, said phase difference detector being adapted to detect thedifference between the phase of the reference signal and the phase ofthe traversing fraction of the measuring signal and to provide a firstoutput signal, the magnitude of the first output signal depending on themagnitude of the difference in phase so detected, the first outputsignal providing a first representation of the amount of dielectric inthe web; and (e) a reflected power detector electrically connected inthe electric circuit between said receptacle, and with said measuringterminal of said power divider, for providing a second output signal,the magnitude of the second output signal depending on the magnitude ofthe reflected second fraction of the measuring signal, the second outputsignal thus comprising a second representation of the amount ofdielectric in the web.
 2. A measuring system as in claim 1, including acontroller adapted to compare the first and second output signals todata stored in said controller, thereby to cancel out the affect of thedistance between said resonant cavity and the dielectric being detected,and to generate a third output signal, the third output signal being amore nearly accurate representation of the dielectric in the web thaneither of the first and second output signals.
 3. A measuring system asin claim 1 wherein the difference in phase, as detected in said phasedifference detector, is a function of dielectric properties extant inthe web.
 4. A measuring system as in claim 1 wherein said electricenergy source comprises, in combination, a varactor-tuned oscillatorhaving a third output signal, a single-frequency crystal oscillatorhaving a fourth output signal, and a phase-locking circuit comprisingsaid varactor-tuned oscillator and said single-frequency crystaloscillator, a portion of said third output signal being routed throughsaid phase locking circuit, said phase locking circuit being configuredto synchronize said varactor tuned oscillator with said single-frequencycrystal oscillator to thereby stabilize the frequency of the thirdoutput signal.
 5. A measuring system as in claim 1 wherein saidreceptacle comprises a tuned transmission line in said resonant cavityand a variable matching device for altering the reactive impedance ofsaid resonant cavity.
 6. A measuring system as in claim 5 wherein saidtuned transmission line comprises first and second transmission rods. 7.A measuring system as in claim 6, said transmission line having inputand output terminals, said variable matching device comprising avaractor diode electrically connected to at least one of said first andsecond transmission rods.
 8. A measuring system as in claim 1, saidreceptacle having a plurality of walls, and an open top, including a topsurface, said measuring instrument comprising a top wall propinquantsaid top surface, said top wall being adapted to transmit microwaveenergy from said resonant cavity with negligible attenuation, a fixedamount of change in phase, and negligible change in frequency, atransmission line in said receptacle, said transmission line beingconstructed of material having a coefficient of thermal expansion nogreater than 4×10⁻⁶ inch per inch length degree Celsius at roomtemperature.
 9. A measuring system as in claim 8, said transmission linebeing constructed of material comprising about 60 to about 65 percent byweight iron, about 34 to about 39 percent by weight nickel, and about0.5 to about 1.5 percent by weight manganese.
 10. A measuring system asin claim 8, said top wall comprising material having a dielectricconstant no greater than about
 5. 11. A measuring system as in claim 8,said top wall comprising material having a dielectric constant nogreater than about
 3. 12. A measuring system as in claim 1 wherein saidphase difference detector comprises a phase locked loop, including avariable phase shifter having a third output signal; a phase detectorhaving a fourth output signal, and having as input signals, the thirdoutput signal of said phase shifter, and the first traversing fractionof the measuring signal as modified by passage through said resonantcavity; and an integrator having, as an input signal, the fourth outputsignal of said phase detector, said integrator providing a fifth outputsignal, including a control signal to said variable phase shifter forforcing the reference signal and the first traversing fraction of themeasuring signal to arrive at said phase detector in quadrature, andthereby forcing the output signal of said phase detector to a null, theoutput signal of said integrator after achieving the null beingrepresentative of the phase difference between the reference signal andthe first traversing fraction of the measuring signal.
 13. A measuringsystem as in claim 5, said electric circuit including a bias teeelectrically connected between said measuring terminal of said powerdivider and said resonant cavity, for providing a bias on said variablematching device, to thereby control the sensitivity, of said tunedtransmission line, to the amount of dielectric in the web.
 14. Ameasuring system as in claim 1, said electric circuit including avariable phase shifter connected in series with said measuring terminalof said power divider, and a variable control input signal to saidvariable phase shifter, for varying the phase length of the measurementpath, thereby to compensate for circuit errors and to establish a knowncalibration condition for taking measurements.
 15. A measuring system asin claim 1, said electric circuit including first and second switchingdevices electrically connected to the input and output terminals,respectively, of said resonant cavity, a first position of saidswitching devices directing the measuring signal to said resonantcavity, a second position of said switching devices directing themeasuring signal to bypass said resonant cavity and pass along analternate signal path, the alternate signal path providing a phase shiftstandard, independent of dielectric adjacent the resonant cavity,whereby the first output signal of said phase difference detectorcorrelates with phase shift caused by circuit elements within saidmeasuring instrument.
 16. A measuring system as in claim 15 wherein thealternate signal path comprises a signal conductor of known phaselength.
 17. A measuring system as in claim 15, said electric circuitincluding a variable phase shifter, having a variable control inputsignal, for varying the phase length of the measurement path, connectedin series with said measuring terminal of said power divider, andwherein, when said first and second switching devices are positioned tobypass said resonant cavity, said phase shifter control input signal canbe varied to change the phase length of the measurement path, therebycompensating for circuit errors and restoring a known calibrationcondition prior to taking measurements.
 18. A measuring system as inclaim 1, including a temperature measuring device, for measuringtemperature in the web, and means to compensate the first output signalfor temperature variations.
 19. A measuring system as in claim 2,including a temperature measuring device, for measuring temperature inthe web, and means to compensate the first output signal for temperaturevariations.
 20. A measuring system as in claim 18 wherein saidtemperature measuring device comprises an infrared detector.
 21. Ameasuring system as in claim 19 wherein said temperature measuringdevice comprises an infrared detector.
 22. A measuring system as inclaim 1, said electric circuit including at least one attenuation deviceand at least one signal amplification device in series with each of themeasurement path and the reference path, said at least one attenuationdevice in each said path being effective to attenuate power reflectedback through the respective circuit elements toward said power divider,said at least one signal amplification device in each said path beingeffective to maintain amplitudes in the respective signals sufficientfor detecting the phase difference between the reference signal and thetraversing fraction of the measuring signal in said phase differencedetector.
 23. A measuring system as in claim 1 wherein said reflectedpower detector comprises a reflected power bridge and a radio frequencydetector.
 24. A measuring system as in claim 1 wherein said reflectedpower detector comprises a reflected power bridge having a third outputsignal, and a radio frequency detector electrically connected to saidreflected power bridge, to measure the magnitude of the third outputsignal, and to provide a fourth output signal dependent on the magnitudeof the third output signal.
 25. A measuring system as is claim 1,including a calibration line of known phase length, and a switch forperiodically and temporarily switching said receptacle out of theelectric circuit and respectively switching said calibration line intothe electric circuit, thereby to periodically recalibrate the electriccircuit based on the known phase length of said calibration line.
 26. Ameasuring system as in claim 25, including a bias device between saidswitch and said measuring terminal of said power divider, thereby toadjust sensitivity of said resonant cavity.
 27. A measuring system as inclaim 25, including a phase shifter between said switch and saidmeasuring terminal of said power divider, thereby to adjust said outputsignal to a desired output when said measuring instrument is away fromconcentrations of dielectric.